Heretofore, various types of deviated wellbores have been drilled from a primary wellbore. One particular type of deviated wellbore, known as a drain hole, is drilled from a primary wellbore through a sharp radius of curvature so as to extend laterally away from the primary wellbore. Normally, although not necessarily, the primary wellbore is essentially vertical and the drain hole, after passing through its sharp radius of curvature extends essentially horizontally away from the primary wellbore out into the producing geologic formation. Drain holes, and the method for drilling same, are fully and completely disclosed in U.S. Pat. Nos. 3,349,845 and 3,398,804.